i definitely learned some things about fiberglass the hard way..

scunny--i think you need a different hardener for cold temperatures, not more of it. the fast hardener will still be pretty slow in cold temps. still, when i made my seatpan, it was in the 30's-40's (cold for portland) and it would take 24 hrs. generally for me to be able to sand it. is your mold a plug, or are you just glassing over it and finishing like i did? i think making a plug is a great idea, but it is one extra step.
i need to get back at my glass tank project (the mold is almost ready, but it's been over a month since i've worked on it...a new K3 has taken the stand for now). my plan is to glass over the foam with one layer of glass cloth, then remove the foam and back it with several layers of chop mat, finishing the surface with body filler. by the way, don't use resin filler. it's hard as steel, and consequently really hard to sand.